In recent years and through partnerships (amongst the San Diego Zoo, the China Conservation and Research Centre for the Giant Panda -Wolong Nature Reserve - and Ocean Park-Hong Kong), we have documented the beneficial effects of enrichment on giant panda well-being (Swaisgood, 1996; Swaisgood et al, 2001; Tepper et al, 2001; see also Chapter 11). Despite our best efforts, sometimes individuals held in enriched environments are still exposed to stressors. Indeed, we have tentatively identified stress as a contributing factor in reproductive failure of at least three female giant pandas at the Wolong facility (Zhang et al., 2004). One significant factor in most zoo environments is noise, such as loud talking by the public, vehicular traffic and construction activities. In 1997, we began to document the impact of noise on the two resident pandas at the San Diego Zoo, an adult male (Studbook, SB, number 381) and an adult female (SB 371) (Owen et al., 2004). Using a sound meter (Model 573; Casella/CEL, Inc., Amherst, NH), we recorded noise levels throughout the day. Behavioural observations were made for two hours (1300 to 1500 hours each day) at a time when noise levels peaked. We recorded behaviours potentially indicative of stress, including locomotion, honking vocalisation, excessive scratching and waiting restlessly at the outside enclosure door, apparently anxious to leave the exhibit. Overnight urine samples were collected daily and analysed for corticoid concentrations, a reflection of the previous day's adrenal activity (see Chapter 8 for methods and explanation).
In an early, crude analysis, we compared the 20 'loudest' and 20 'quietest' days for differences in behavioural and hormonal indices. These preliminary data suggested no major impact of noise on the giant panda (Swaisgood & Borst, 1998). A more detailed analysis of a larger four-year data set did document several significant noise impacts (Owen et al, 2004). First, we defined loud days as the loudest 25% of days (as determined by recorded amplitude levels) and quiet days as the quietest 25%. In one analysis, we examined the average amplitudes for the entire day (loud days = 72 decibels or dB; quiet days = 65 dB). In another, we examined the very loudest sounds heard during the loudest 1% of one-minute intervals (loud days = 81 dB; quiet days = 70 dB). Therefore, this latter analysis examined the impact of the loudest 15 minutes of noise exposure on a given day. During loud days, this maximum noise level was approximately 15 times higher than maximum noise on quiet days. Because decibels are measured on a logarithmic scale, a 3-dB change reflects a doubling of noise energy, i.e. it sounds twice as loud. Although duration of individual noise events was not examined, it is helpful to use the average decibel level for the entire day as a measure of 'chronic' noise exposure and the 15 minutes of the loudest 1% of noise as an index of'acute' noise.
In general, loud days were associated with high rates of locomotion and honking, restless manipulation of the enclosure door, increased scratching and/or increased concentrations of urinary glucocorticoids. Data also suggested that acute exposure to very loud noise reliably induced behavioural distress, whereas chronically moderate noise was required to activate the HPA and to increase urinary corticoid excretion. Indices of stress were also stronger for low-pitched sound (16-64 hertz or Hz) compared to medium (125-500 Hz)- or high-pitched (1000-16000 Hz) noise. The female that we studied showed greater behavioural sensitivity to noise during oestrus and lactation than during nonreproductive periods and pregnancy/pseudopregnancy. In contrast, urinary glucocorticoid excretion profiles were more dynamic during nonreproductive periods, suggesting that adrenal responsiveness to noise was suppressed during intervals of heightened ovarian activity (as has been found for other species; Cook, 1997). If this observation holds true, using urinary corticoids to monitor stress during crucial reproductive periods may be misleading. Finally, it was clear from our analyses that the two giant pandas differed markedly in noise responsiveness, especially hormonally. For example, only the female produced significantly different glucocorticoid patterns in the urine in response to this particular disturbance.
Although there was a significant noise effect on behaviour and adrenal hormone response, the overall impact on what might be considered well-being appeared admittedly minor. We found that only 15% of a giant panda's total time was spent expressing these mild behavioural indicators of stress. Additionally, when excreted corticoids were elevated, increases were only about 10 to 40% above baseline. Nonetheless, we were able, through an assessment of multiple variables, to document some change in behavioural and physiological function to an environmental factor. Thus, it makes sense that more detailed studies be explored to determine if different (and perhaps more severe) perturbations can influence health and well-being, especially at sensitive intervals, such as at implantation and parturition. Even commonly encountered noise in a zoo atmosphere clearly can activate the stress response system in the giant panda and, therefore, should be monitored and mitigated; and, if noise can be aversive to pandas that have had years to habituate in captivity, then their wild counterparts may be even more likely to respond negatively to such a disturbance. Potentially, noise (caused by encroaching people via mining, farming or ecotour-ism) could cause pandas to abandon good habitat, dens and cubs.
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